Mercury cathode tube



MERCURY CATHODE TUBE Filed Feb. l5, 1937 Parenteel May 31, 1938 UNITED STATS EBATN GFFICE MERCURY CATHODE TUBE 'Iom .lurriaansa Eindhoven, Netherlands, as-

signor to N. V. Philips Gloeilampenfabrieken,

Eindhoven, Netherlands Claims.

My invention relates to mercury-cathode tubes, such as mercury arc rectifiers and relays, and more particularly to the anchoring of the cathode spot of such tubes.

To stabilize the operation of such tubes, anchoring members are used to prevent the cathode spot from wandering over the surface of mercury and to prevent splashing of the mercury. If the portion of the envelope in the vicinity of the cathode is of metal, or of glass coated with a conductive deposit such as mercury, such members prevent the cathode spot from passing over the surface of the mercury and reaching the conductive wall portion. This greatly reduces the possibility of damage to the envelope, and

especially to the metal-glass seal of envelopes having a metal portion and a glass portion fused together.

As the cathode spot .generally settles at the line of separation between the anchoring member and the mercury, i. e. at the cathode line, the surface at this point must be of perfectly pure metal free from oxides to ensure proper anchoring action. This condition can be satisfied in a simple manner by making the anchoring member of a metal capable o f amalgamating with mercury, as this amalgamation removes the surface layer and its impurities. However, metals which amalgamate sufficiently with mercury, for instance copper, dissolve so rapidly in mercuryespecially at the physically highly-stressed point at which the cathode spot settles-that the life of the member is reduced to such extent that the tube is soon rendered unserviceable.

If, to ensure a satisfactory life, the anchoring member is made of a material which is substantially insoluble in mercury, the anchoring properties are either very poor, or can be developed only with great difficulty. Thus, a completely satisfactory solution of this problem in a simple manner was hitherto impossible, and a suiiicient life of such members and of the tubes could be ensured only by using extremely pure and expensive metals such as platinum, or by resorting to extremely complicated purifying methods during the manufacture of the tube.

The object of my invention is to overcome the above diiiiculties and to produce an anchoring member which has a long life and satisfactory anchoring properties.

According to the invention, I form the anchoring member from a metal or a metal-alloy whose dissolving speed in mercury during the passage of discharge current is less than about 5, preferably about 1/40, of that of copper, and which (Cl. Z50-27.5)

amalgamates better than does iron or molybdenum.

The term dissolving speed in mercury as used herein and in the claims, is to be understood to mean the loss in material of, the anchoring mem- 5 ber due, inter alia, to amalgamation with the mercury and to disintegration by the discharge. per unit of time and per unit of. arc current during the operation of the tube.

Anchoring members of such materials have suiciently long life for all practical purposes, and the settling point of the cathode spot upon the anchoring member is formed with full security and without taking additional measures, so that the manufacture of the tube is not complicated. Furthermore, the materials used are standard and can be obtained at a comparatively low cost.

As the dissolving process and any corrosion phenomena at the settling point of the cathode y spot depend to a large extent upon the temperature, it is essential to have a good dissipation of heat from this point. For this purpose I prefer to locate the anchoring member in the middle of the mercury cathode, and in good heat-transierring relationship with the envelope.

In order that my invention may be clearly understood and readily carried into effect, I shall describe same more fully with reference to the accompanying drawing, in which: ,3o

Figure l is a sectional side-view of a mercuryvapor rectifier embodying the invention;

Fig. 2 is a sectional View of an anchoring member according to the invention.

The rectifier shown in Figure 1 comprises an 35 envelope consisting of a cup-shaped metal member l, for instance of chrome iron, and a glass member 2 hermetically fused together at I1. Disposed in the bottom of member l is a mercury cathode 3, whereas a main anode 8 is supported 40 from the lower' end of a conductor 6 Whose upper end is secured to a metal disc 4 hermetically sealed in glass portion 2 and carrying a terminal. Supported from conductor 6 and surrounding anode 8 is a cylindrical screen II serving to 45 protect the higher internal surfaces of portion I and seal Il from the detrimental effects of the discharge.

Supported by screen Il, preferably of sheet molybdenum,'is an insulating tube 20 through 50 the bore of which extends a conductive rod I9 carrying on its lower end an auxiliary anode 9. The anode 9 is adapted to be moved in the direction of the double-headed arrow, and for this purpose the upper end of rod I9 carries a plunger 55 I8 of magnetic material electrically connected` through a compression spring 22 to a core 2| of a magnetic material. Core 2l is supported `from the lower end of a conductive rod 1 secured to a disc 5 hermetically sealed in glass portion 2. Outside the envelope and surrounding core 2I is coil III which serves to raise anode 9 from the surface of the mercury.

Surrounding metal member I is a cooling jacket I 2 having an inlet opening I3 and an outlet opening I4, and through which a. circulating cooling medium, such as Water, is circulated in the direction of the arrows during operation of the rectier. Jacket I3 is secured to metal member I by a copper bolt I5 secured, for instance, by Welding to the bottom of member I and serving to supply current to cathode 3.

Centrally disposed in the mercury'cathode 3 is an anchoring member I6. According to the invention, I form member I6 of a metal or metal `alloy Whose dissolving speed in mercury during the discharge of the discharge current is at `the utmost Tmfand preferably about 1/40, of that of copper, :and which'amalgamates better Vthan does iron or molybdenum. As a suitable material for this purpose I prefer to use nickel or an --alloy substantially constituted by this metal.

To insure good dissipation of heat from memberV I6, the entire lower surface thereof is in direct metallic contact with the bottom of the memberwl, and for instance, Welded thereto. The member I5, which is of large size and of a good .heat-.transmitting material, such as copper, is

secured, for instance welded, to the lower surface of .member I land thus aids in the dissipation of .heat from the anchoring member I6.

As shown in Figure 1, member I6 is shaped as a disc; however it maybe given various other shapes, for instance asa ring 23, as shown in Fig. .2. The cathode line inside a ringshaped member,.in contradistinction to that around a disc shaped member, will show a tendency to grow longer as a result of the gradual erosion of the `member so that its current carrying capacity is not impaired with the increase of the age of .the tube. Furthermore, member I6 may have aroundedor roughened upper surface, and it is sometimes of advantage to use a porous structure.

While I have described my invention in connection with specicexamples and applications, I doV .not Wish to be limited ythereto but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What I claim is:-

1. A mercury-cathode tube comprising an envelope having a wall portion of mercury-resistant metal forming part of the bottom thereof, electrodes within said envelope including a mercury cathode Within the bottom part, and a massive cathode-spot anchoring member partly Within said mercury cathode and carried by said metal wall portion, said member consisting of a metallic material substantially of nickel.

2. A mercury-cathode tube comprising anenvelope having a wall portion of mercury-resistant metal forming part of the bottom thereof, electrodes within said envelope including a mercury cathode within the bottom part, and a massive cathode-spot anchoring member of nickel partly within said mercury cathode and carried by said metal wall portion.

3. Afmercury-cathode tube comprising an enveloperhaving a wall portion of mercury-resistant metal forming part of the bottom thereof, electrodes within said envelope including a mercurycathode within the bottom part, and a massive cathode-spot anchoring member partly within said mercury cathode and secured to said metal wall portion in good heat-transferring relationship, said member consisting of a metallic material substantially of nickel.

4. A mercury-cathode tube comprising an envelope having a wall portion of mercury-resistant metal forming part of the bottom thereof, means for artificially cooling said metal wall portion, electrodes -within said envelope including a mercury cathode Within the bottom part, and a massive cathode-spot anchoring member partly With in said mercury cathode and secured to said wall portion in good heat-transferring relationship, said member consisting of a lmetallic material substantially of nickel.

.5. A mercury-cathode tube comprising an envelope having a wall portionof mercury-resistant metal forming part of the bottom thereof, electrodes withinvsaid envelope including-a mercury cathode within the bottom part, and a massive cathode-spot anchoring vmember partly within said mercury cathode andcarried by said metal ,Wall portion, said member having an annular shapeand consisting of a metallic material substantially of nickel.

rI'OM JURRIAANSE. 

